Surface plasmon polaritons (SPPs) confine and enhance local electromagnetic fields near surfaces of metallic nano structures at optical frequencies. Given their ability to propagate along sub-diffractive metallic waveguides, SPPs have been used in electronic plasmonic devices for information processing and computing.
Yet, these applications use large external light sources, e.g., monochromatic lasers. To minimize the size of light sources and, ultimately, the size of plasmonic devices, plasmons have been excited on-chip using electrically driven light sources such as light emitting diodes, silicon spheres, and single carbon nanotubes, instead of bulky lasers.
To date, surface plasmons have been directly excited by tunnelling electrons in metal-insulator-metal junctions based on metal oxides or scanning tunnelling microscopes using vacuum or molecular tunnelling barriers. During the tunnelling process, most of the electrons tunnel elastically. However, some of the electrons tunnel inelastically and couple to a plasmon mode. These electronic plasmon sources often require use of optical elements, e.g., gratings and prisms, thereby increasing their sizes.
There is a need to develop a new method for producing electronic plasmons without the above-described drawbacks.